Easily available chromium(II) acetate was used for an entry into chromium chemistry: sodium tetraisopropylcyclopentadienide (Na4Cp), sodium 1,2,4‐tri(tert‐butyl)cyclopentadienide (NaCp′′′), or lithium pentaisopropylcyclopentadienide (Li5Cp) convert the acetate to the acetate‐bridged dimers [4CpCr(µ‐OOCCH3)]2 (1a), [Cp′′′Cr(µ‐OOCCH3)]2 (1b), or [5CpCr(µ‐OOCCH3)]2 (1c) in yields well above 70 %. These acetates could be converted into the halide‐bridged dimers [4CpCr(µ‐Cl)]2 (2a), [4CpCr(µ‐Br)]2 (3a), [Cp′′′Cr(µ‐Br)]2 (3b), or [5CpCr(µ‐Br)]2 (3c), [4CpCr(µ‐I)]2 (4a), or [Cp′′′Cr(µ‐I)]2 (4b) with the corresponding trimethylsilyl halides in nearly quantitative yield. With bis(trimethylsilyl)sulfate the acetate 1a gave crude bis(tetraisopropylcyclopentadienylchromium)sulfate (5a). From the bromide 3b and sodium bis(trimethylsilyl)amide the mononuclear chromium(II) silylamide [Cp′′′CrN(SiMe3)2(THF)] (7b) was obtained as a tetrahydrofuran adduct. Upon reaction with sodium azide, the iodide 4a afforded the tetranuclear chromium(IV) nitride cubane [(4CpCr)3(µ3‐N)4CrOH] (8a) after extraction with heptane containing traces of water. The analogous chromium nitride derivative [(Cp′′′Cr)3(µ3‐N)4CrBr] (9b) was obtained from the bromide 3b and sodium azide.

Alkylcyclopentadienylchromium(II) bromide dimers [Cp‴Cr(μ-Br)] 2 and [ 5 CpCr(μ-Br)] 2 (Cp‴ = tri(tert-butyl)cyclopentadienide, 5 Cp = pentaisopropylcyclopentadienide) have been used as starting compounds for replacement of bromide with methyl, hydride, phenyl, phenylacetylide, cyanide, or tetrahydroaluminate anions and afforded dinuclear chromium(II) complexes except for cyanide and tetrahydroaluminate, where tetranuclear products were isolated. Mononuclear chromium complexes have been synthesized by N-heterocyclic carbene addition to the bromide complex or by bromide substitution with a cyclopentadienyl or another alkylcyclopentadienyl ligand. Strong antiferromagnetic coupling with J 1,2 = −206 cm −1 of two high-spin Cr(II) central atoms has been found for the dinuclear hydride [Cp‴Cr(μ-H)] 2 , which was obtained during reactions with isopropylmagnesium chloride via β-hydride elimination and was also found after attempted potassium reduction of the chromium(II) starting compound. Diamagnetic behavior was observed only for the tetranuclear aluminumtetrahydro-tri(tert-butyl)chromate(II).

The chromium(II) tricarbonyl methyl complex [Cp′′′Cr(CO) 3 CH 3 ] (1, Cp′′′ = η 5 -C 5 H 2 tBu 3 -1,2,4) was obtained from chromium hexacarbonyl, NaCp′′′, and methyl iodide. 1 was found to establish an equilibrium with the dicarbonyl acetyl isomer [Cp′′′Cr(CO) 2 (COCH 3 )] in solution via reversible, slightly endothermic methyl migration from chromium to a carbonyl ligand with ΔH ca. 3.6 kJ/mol and E a ca. 49.5 kJ/mol. Phosphorus pentachloride oxidized 1 to the green, dinuclear tetrachloro complex [Cp′′′CrCl(μ-Cl)] 2 (2), which was crystallized as the blue-green chromium(III) half sandwich complex [Cp′′′CrCl 2 -(THF)] (3) in the presence of tetrahydrofuran vapor. Attempted sublimation of the known chromium(II) iodo complex [ 4 CpCr-(μ-I)] 2 resulted in a redox reaction with formation of the chromium(III) iodo dimer [ 4 CpCrI(μ-I)] 2 , whose tri(tert-butyl)-[a] FB Chemie der TU Kaiserslautern